A continuing problem attendant with the use of optical glasses, goggles, face shields, and other optical devices in both medical and industrial applications is fogging of the viewing substrate. The warm, moist air exhaled by the wearer will condense on relatively cool surfaces that are in close proximity to the nose or mouth of the user. Condensate droplets will fog the viewing surfaces, which may seriously impair vision.
Various approaches have been attempted to alleviate the problems due to fogging on goggles and glasses. For example, passive coatings for surfaces have been described that function by absorbing moisture and/or spreading the moisture across a surface to eliminate droplet formation that leads to fogging. Examples of passive coatings have been described in U.S. Pat. Nos. 4,767,671 and 5,668,618. More recently, active approaches have been suggested for use in preventing condensate that leads to misting or fogging of a surface. For example, U.S. Pat. No. 6,470,696 describes a device including two thermal sensors, one in contact with a surface and the other in contact with a cooling device. The device also includes a humidity sensor. A circuit causes a condensation removal mechanism to be activated for removing liquid from the surface when the humidity sensor indicates the presence of condensation based upon the readings of the thermal sensors. In another example, German publication DE 3323670 describes a visor that includes a strip of conductive material attached to the visor and terminals for electrical connection to a current source to heat the visor via the strip and prevent misting of the visor.
While the above describe improvement in the art, room for additional improvement exists. What are needed in the art are active coatings for prevention of condensation, for example, fog, on surfaces.